Thiocarbamate herbicidal compounds have been commercially sold since the 1950,s and are very effective in controlling weeds in a variety of crops such as rice, potatoes, sugarbeets, sunflowers and tobacco. These herbicidal compounds have been described in a variety of patents such as U.S. Pat. Nos. 2,913,317, 2,919,182, 3,037,853, 3,175,897, 3,185,720, 3,198,786 and 3,582,314.
Preferred thiocarbamate compounds of this invention have the following structural formula: ##STR1## wherein R is ethyl, n-propyl, isopropyl, 2,3-dichloroallyl, 2,3,3-trichloroallyl, benzyl or p-chlorobenzyl, preferably ethyl, n-propyl or isopropyl;
R.sup.1 is C.sub.1 -C.sub.6 alkyl, preferably C.sub.2 -C.sub.4 alkyl; and PA1 R.sup.2 is C.sub.2 -C.sub.6 alkyl, preferably ethyl, propyl, isopropyl, n-butyl, isobutyl, dimethylpropyl and cyclohexyl; or PA1 R.sup.1 and R .sub.2 together are a C.sub.3 -C.sub.6 alkylene group optionally substituted with methyl, preferably pentylene.
Thiocarbamate compounds that have been sold commercially since 1958 are as follows:
______________________________________ Chemical Name Common Name ______________________________________ S-ethyl dipropyl thiocarbamate EPTC S-ethyl diisobutyl thiocarbamate butylate S-ethyl N-cyclohexyl-N-ethyl thiocarbamate cycloate S-ethyl hexahydro-1H-azepine-1-carbothioate molinate S-propyl dipropyl thiocarbamate vernolate S-propyl butylethyl thiocarbamate pebulate S-2,3,3-trichloroallyl diisopropyl thiocarbamate triallate S-2,3-dichloroallyl diisopropyl thiocarbamate diallate S-p-chlorobenzyl diethyl thiocarbamate thiobencarb Ethyl-1-hexahydro-1,4-azepine-1-carbothioate byram S-benzyl N,N-di-sec.-butyl thiocarbamate tiocarbazil S-benzyl N-ethyl-N-2,3-dimethylpropyl thio- esprocarb carbamate ______________________________________
Commercially, most thiocarbamate compounds are prepared by first reacting appropriately substituted mercaptan (ethyl mercaptan) with phosgene to give a carbamoyl chloride. Next, the substituted chlorothio formate (ethyl chlorothioformate) is reacted with an appropriately disubstituted amine (di-n-propylamine) to give the desired thiocarbamate compound (S-ethyl di-n-propyl thiocarbamate).
During the manufacture of technical thiocarbamate compounds, several odorous compounds are formed that contaminate the final product. Also, these odorous compounds sometimes are present in starting materials such as the substituted mercaptans and they are carried through the manufacturing process steps to the final thiocarbamate product. Additionally, upon storage of thiocarbamate compounds, they tend to slightly degrade or decompose to produce odorous compounds.
These odorous compounds are believed to have the structural formulae: EQU R--S--S--R, R--S--S--S--R, and R--S--S--S--S--R
wherein R is as defined above, and will depend upon the particular thiocarbamate compound that is being manufactured. Especially odorous compounds are believed to have the structural formula EQU R--S--S--R
wherein R is ethyl, n-propyl, benzyl, p-chlorobenzyl, 2,3-dichloroallyl or 2,3,3-trichloroallyl.
One of the most odorous compounds is believed to be diethyl disulfide (DDS).